Research On Rapid Detection Of Urban Hidden Geological Hazards Based On Transient Electromagnetic Method

Hidden geological disasters such as ground fissures and underground cavities in cities constantly threaten the safety of people’s lives and property,limiting the efficient use of urban space.In the field of underground exploration,transient electromagnetic method is a nondestructive and economical detection method.Compared with traditional drilling exploration and direct excavation exploration methods,it has the advantages of time-saving,labor-saving,and safe and reliable.This article focuses on the application of transient electromagnetic method in urban hidden geological disasters,and the main content is as follows:Firstly,the application of transient electromagnetic method in shallow geological disasters was analyzed,and the influencing factors of blind spots in shallow transient electromagnetic method detection were analyzed.A Simulink simulation model of a transient electromagnetic instrument was built to explore the impact of parameter changes in the transmitting and receiving coils on the secondary field.A study was conducted on the fast shutdown technology of transient electromagnetic method transmitters,and an active constant voltage clamp shutdown circuit was designed.Compared with traditional shutdown technology,its shutdown time is greatly shortened.To solve the problem of mixing primary and secondary fields during shutdown,a method for removing primary fields during shutdown is proposed.We have built a Maxwell simulation model for underground cavities,proposed a fast calculation method for apparent resistivity based on neural networks,and conducted simulation analysis on the underground cavity model.We have obtained a cross-sectional map of the apparent resistivity of the underground cavity,which can be used to determine the position and shape of the underground cavity.Secondly,a design scheme for a transient electromagnetic receiver was proposed.We have designed the overall instrument plan and clarified the working relationships between each part;Design the hardware separately from the power module,signal acquisition module,screen display module,and LoRa communication module.The design scheme selects the STM32F429 microprocessor as the main control chip,which sends instructions to the transmitting coil to excite a field,while controlling the acquisition module to collect transient electromagnetic signals.In the design of the acquisition module scheme,a signal conditioning circuit was designed to meet the requirements of shallow transient electromagnetic detection,including an eight channel graded amplification acquisition circuit based on AD7606 and a low-pass filtering circuit.The screen display and LoRa wireless communication module scheme were designed,and functions such as AD acquisition,LoRa transmission,and upper computer display were programmed and debugged.Finally,conduct on-site exploration and verification of known ground fissures.Based on the basic information of ground fissures and the performance of the experimental device,an experimental plan was designed and on-site exploration experiments were conducted.The analysis of the experimental results showed that the information on the strike depth of ground fissures detected using transient electromagnetic method was highly consistent with the known information of ground fissures,verifying the reliability and accuracy of the application of transient electromagnetic method in ground fissure detection.